Bearing apparatus

ABSTRACT

An outer ring is provided with a key groove radially extending from an inner diameter to an outer diameter on an end surface thereof. A key member includes an annular body, an inwardly projecting part which is provided on an inner periphery of the annular body and adapted to be inserted into the key groove of the outer ring, and an outwardly projecting part which is provided on an outer periphery of the annular body and adapted to be inserted into a key groove of an axle box.

BACKGROUND OF THE INVENTION

The present invention relates to a bearing apparatus, and moreparticularly, to the bearing apparatus in which an outer ring issupported by an axle box so as to move in an axial direction.

Conventionally, as a bearing apparatus to be used in a motor, forexample, there has been known a bearing apparatus including a pair ofrolling bearings, one of which is positioned at a fixed side and theother is positioned at a free side, and so constructed that an outerring of the rolling bearing at the free side is fixed to an axle boxprovided with a key groove in a manner restrained from rotation by meansof a key member, and supported so as to move in an axial direction,thereby to absorb a difference in thermal expansion of a rotation shaftduring operation (JP-A-2004-239388). In JP-A-2004-239388, it isdisclosed that a key hole in a columnar shape or in a square pillarshape is provided on an outer peripheral surface of the outer ring ofthe bearing, and a lower end of a key member in a columnar shape or in asquare pillar shape is inserted into the key hole, while an upper partof the key member is movably inserted into the key groove in the axlebox, thereby permitting the outer ring and the axle box to move within arange of the key groove.

Although ceramics are preferably employed as material for the rollingbearing which is used in an environment where thermal expansion must betaken into consideration, it is difficult to work the keyhole in acolumnar shape or in a square pillar shape in brittle material such asceramics. Therefore, there is a problem that the bearing apparatusdisclosed in JP-A-2004-239388 can be applied only in case where metallicmaterial such as bearing steel is employed as the material for thebearing, but cannot be applied in case where the brittle material isemployed.

SUMMARY OF THE INVENTION

In view of the above, it is an object of the invention to provide abearing apparatus in which an outer ring can be easily worked, eventhough it is formed of brittle material, so that the outer ring can berestrained from rotation but can move in an axial direction.

According to a first aspect of the invention, there is provided abearing apparatus to be supported by an axle box which includes a keygroove, the bearing apparatus comprising:

an outer ring which includes a first key groove extending from an innerdiameter to an outer diameter of an end surface of the outer ring;

an inner ring;

rolling elements rollably interposed between the outer and inner rings;and

a key member which includes an annular body, a first inwardly projectingpart which is provided on an inner periphery of the annular body andadapted to be inserted into the first key groove of the outer ring, andan outwardly projecting part which is provided on an outer periphery ofthe annular body and adapted to be inserted into the key groove of theaxle box.

In the bearing apparatus according to the first aspect of the invention,although it would be sufficient that the key groove of the outer ring isprovided at only one position, the key grooves may be provided at aplurality of positions. In any case, the one key groove is formed so asto extend from the inner diameter to the outer diameter withoutnecessity of leaving a part (a peripheral part or a bottom part of ahole). Accordingly, it is possible to easily form the key groove bycutting work, even though the outer ring is formed of brittle material.In case of conducting the cutting work, there is no difference inworking trouble between the work for forming the key groove extendingfrom the inner diameter to the outer diameter and the work forcontinuously cutting the outer ring from one outer diameter to the otherdiameter, and therefore, it is possible to conduct the latter work andthen, to form the key grooves extending from the inner diameter to theouter diameter at two positions separated from each other by 180 degree.

Usually, the inwardly projecting part to be inserted into the key grooveof the outer ring is not permitted to move both in a circumferentialdirection and in an axial direction for restraining the rotation of theouter ring. However, the inwardly projecting part may be made movable tosome extent in the circumferential direction, because rotation detentfunction can be attained even though there is a play in thecircumferential direction. Moreover, the outwardly projecting part to beinserted into the key groove of the axle box is usually not permitted tomove in the circumferential direction but can move in the axialdirection. In this manner, the outer ring is restrained from rotationbut can move in the axial direction with respect to the axle box, andfavorably support the rotation shaft which is liable to vary in lengthdue to thermal expansion. In case where the outer ring need not move inthe axial direction, the outwardly projecting part may be made so as notto move in the axial direction too. In this manner, the outer ring canbe fixed to the axle box.

The annular body of the key member includes, for example, a cylindricalpart and an inwardly directed flange part which is provided at one endof the cylindrical part. The cylindrical part covers an outer peripheralsurface of the outer ring, and the inwardly directed flange part coversone end surface of the outer ring. In this case, the cylindrical partmay be fitted to the outer ring by press fitting or may be looselyfitted. The annular body of the key member may be modified according tothe shape of the axle box. For example, in case where there is noclearance between the axle box and the outer ring, the annular body maybe formed in a square shape in cross section, and butted against the oneend surface of the outer ring. In any case, the key member can beattached to the outer ring in advance, by inserting its inwardlyprojecting part into the key groove of the outer ring, and thus, theouter ring provided with the key member can be handled as a singlecomponent.

According to a second aspect of the invention, there is provided abearing apparatus to be supported by an axle box which includes a keygroove, the bearing apparatus comprising:

an outer ring which has an outer peripheral surface formed into aneccentric surface;

an inner ring;

rolling elements rollably interposed between the outer and inner rings;and

a key member which includes an annular body having an inner peripheralsurface corresponding to the eccentric surface of the outer ring and anouter peripheral surface in a cylindrical surface, and an outwardlyprojecting part which is provided on an outer periphery of the annularbody and adapted to be inserted into the key groove of the axle box.

According to the bearing apparatus of the second aspect of theinvention, the inner peripheral surface of the annular body of the keymember lies along the eccentric surface of the outer ring thereby torestrain the outer ring from rotation. The outwardly projecting part tobe inserted into the key groove of the axle box is usually not permittedto move in the circumferential direction but permitted to move in theaxial direction. In this manner, the outer ring is restrained fromrotation but can move in the axial direction with respect to the axlebox, and favorably support the rotation shaft which is liable to vary inlength due to thermal expansion. In case where the outer ring need notmove in the axial direction, the outwardly projecting part may be madeso as not to move in the axial direction too. In this manner, the outerring can be fixed to the axle box.

In the bearing apparatus according to the first and second inventions,the key member is formed of metal such as steel, in some cases. In thiscase, it is possible to coat the outer peripheral surface of the keymember which slides with respect to the axle box withpolytetrafuluoroethylene (PTFE), diamond-like carbon (DLC), etc. whichare excellent in abrasion resistance and sliding performance. In someother cases, the key member is formed of synthetic resin such aspolyetherether ketone (PEEK). In this case, the key member can be formedof synthetic resin by injection molding, and hence, the key member invarious shapes can be easily formed. Moreover, it is possible to obtainthe key member which is integrally formed with the outer ring, bymolding the outer ring out of resin, employing resin molding process. Inthis manner, it becomes easier to produce the key member and handle thekey member thereafter. The bearing apparatus according to the secondinvention is particularly suitable in case of employing the resinmolding process.

As the rolling bearing constituting the bearing apparatus, a deep grooveball bearing or an angular ball bearing in which the rolling element isa ball may be used, for example. However, the rolling bearing is notlimited to them.

In some cases, an intermediate housing which moves integrally with theouter ring is interposed between the axle box provided with the keygroove and the outer ring. In this case, the intermediate housing isdeemed as a part of the outer ring, and at least one key grooveextending from an inner diameter to an outer diameter may be formed onan end surface of the intermediate housing. On the other hand, the keymember may include an annular body, an inwardly projecting part to beinserted into the key groove of the intermediate housing, and anoutwardly projecting part provided on an outer periphery of the annularbody and adapted to be inserted into the key groove of the axle box.

According to the bearing apparatus of the invention, it is possible toeasily work the outer ring, even though it is formed of brittlematerial, and by attaching this outer ring to the axle box by way of thekey member, the rotation of the outer ring can be restrained, while theaxial movement of the outer ring is permitted.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a vertical sectional view showing a bearing apparatus in afirst embodiment according to the invention.

FIG. 2 is an exploded perspective view of the bearing apparatus in FIG.1.

FIG. 3 is a vertical sectional view showing a bearing apparatus in asecond embodiment according to the invention.

FIG. 4 is an exploded perspective view of the bearing apparatus in FIG.3.

FIGS. 5A and 5B are perspective views showing a bearing apparatus in athird embodiment according to the invention.

FIGS. 6A and 6B are perspective views showing a bearing apparatus in afourth embodiment according to the invention.

FIG. 7 is a vertical sectional view showing a bearing apparatus in afifth embodiment according to the invention.

FIG. 8 is an exploded perspective view of the bearing apparatus in FIG.7.

FIG. 9 is a vertical sectional view of a bearing apparatus in a sixthembodiment according to the invention.

FIG. 10 is a view of a key member in the sixth embodiment as seen in theaxial direction.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Now, embodiments of the invention will be described referring to thedrawings. It is to be noted that terms “right and left”, and “upper andlower” in the following description respectively mean a right side and aleft side, and an upper side and a lower side in a vertical sectionalview as shown in FIGS. 1 and 3.

First Embodiment

FIGS. 1 and 2 show the bearing apparatus according to a first embodimentof the invention.

A bearing apparatus 1 is provided between an axle box 2 and a rotationshaft 3, and includes an outer ring 4 supported by the axle box 2, aninner ring 5 which rotates with the rotation shaft 3, a plurality ofballs (rolling elements) arranged between the two rings 4 and 5, a cage7 for holding the balls 6, and a key member 10 in an annular shape whichis interposed between the axle box 2 and the outer ring 4 so that theouter ring 4 can be supported by the axle box 2 so as not to rotate butso as to move in an axial direction.

The axle box 2 is formed of metal, and provided with a key groove 2 aextending in the axial direction. Because the outer ring 4 is movable inthe axial direction within a range defined by the key groove 2 a, therotation shaft 3 which is liable to vary in length due to thermalexpansion is rotatably supported by the axle box 2.

The inner ring 5 is clamped between a flange part 3 a provided at aright end of the rotation shaft 3 and a spacer 8, thereby to be fixed tothe rotation shaft 3. The outer ring 4 is urged to the right by apressurizing spring 9, but not fixed, and allowed to move in the axialdirection.

The outer ring 4, the inner ring 5, and the balls 6 are formed ofceramics so that variation due to thermal expansion may be small.

In case where the outer ring is formed of metal, it would be sufficientthat a key may be inserted into a key hole which is formed in the outerring, and this key which has been inserted into the key hole may bemovably inserted into a key groove formed in the axle box. However, inthis bearing apparatus 1, it is difficult to work the key hole in theouter ring 4, because the outer ring 4 is formed of ceramics which isbrittle material. Considering workability of the outer ring 4 which isformed of ceramics, it is possible to easily work a key groove, providedthat the key groove extends from one end to the other end in the axialdirection on an outer peripheral surface of the outer ring 4, or in casewhere the key groove extends from an inner diameter to an outer diameterat one end of the outer ring 4. In case where the key groove extendsfrom the one end to the other end in the axial direction, there is suchpossibility that the key member may fall, when the outer ring isdisplaced in the axial direction. Therefore, in this bearing apparatus1, a key groove 11 is so formed as to radially extend from the innerdiameter to the outer diameter on a left end surface of the outer ring4.

The key member 10 includes an annular body 12 having a cylindrical part12 a and an inwardly directed flange part 12 b which is provided at aleft end of the cylindrical part 12 a, an outwardly projecting part 13which is provided in an upper part of an outer peripheral surface of thecylindrical part 12 a of the annular body 12 along its entire length inthe axial direction and adapted to be inserted into the key groove 2 aof the axle box 2, and an inwardly projecting part 14 which is providedon a right surface of the inwardly directed flange part 12 b of theannular body 12 and adapted to be inserted into the key groove 11 of theouter ring 4.

The outwardly projecting part 13 is so shaped as to move in the axialdirection in the key groove 2 a of the axle box 2, while the inwardlyprojecting part 14 is so shaped as not to move both in a circumferentialdirection and inwardly in the axial direction. Therefore, in FIG. 1,when a length of the rotation shaft 3 has varied due to thermalexpansion, the outer ring 4 moves in the axial direction along the axlebox 2, whereby the variation due to the thermal expansion can beabsorbed.

The cylindrical part 12 a of the key member 10 has an outer diameterwhich is substantially equal to an inner diameter of the axle box 2, andan inner diameter which is substantially equal to an outer diameter ofthe outer ring 4. At the same time, a length of the cylindrical part 12a in the axial direction is equal to a length of the outer ring 4 in theaxial direction plus a length of the inwardly directed flange part 12 bin the axial direction. As the results, the cylindrical part 12 a of thekey member 10 covers an entirety of the outer peripheral surface of theouter ring 4, and the inwardly directed flange part 12 b of the keymember 10 covers an entirety of a left end surface of the outer ring 4.Therefore, by fitting the key member 10 to the outer ring 4 from theleft, the cylindrical part 12 a of the key member 10 is engaged with theouter peripheral surface of the outer ring 4, and the inwardlyprojecting part 14 is engaged with the key groove 11 of the outer ring4, whereby the key member 10 and the outer ring 4 can be handled as anintegral body.

Second Embodiment

FIGS. 3 and 4 show the bearing apparatus according to a secondembodiment of the invention.

The bearing apparatus 1 in the second embodiment is different from thefirst embodiment only in a structure of a key member 20. In thefollowing description, the same members as in the first embodiment aredenoted with the same reference numerals, and explanation of the memberswill be omitted.

In the first embodiment, it is possible to stably fit the key member 10to the outer ring 4, because the cylindrical part 12 a of the key member10 is engaged with the outer peripheral surface of the outer ring 4. Onthe other hand, in case where the first embodiment is applied to theexisting bearing apparatus, it is necessary to modify the bearingapparatus so that the inner diameter of the axle box 2 may be increasedor the outer diameter of the outer ring 4 may be reduced, because thecylindrical part 12 a is interposed between the axle box 2 and the outerperipheral surface of the outer ring 4.

The bearing apparatus 1 in the second embodiment can be applied to theexisting bearing apparatus, without modifying the inner diameter of theaxle box 2 and the outer diameter of the outer ring 4. The key member 20includes an annular body 22 having a rectangular shape in cross section,an outwardly projecting part 23 which extends to the right from an upperpart of an outer periphery of the annular body 22 and adapted to beinserted into the key groove 2 a of the axle box 2, and an inwardlyprojecting part 24 which is provided on a right surface of the annularbody 22 and adapted to be inserted into the key groove 11 of the outerring 4.

Specifically, the annular body 22 has the same shape as the inwardlydirected flange part 12 b of the key member 10 in the first embodiment,except that the cylindrical part 12 a is omitted from the key member 10in the first embodiment. The outwardly projecting part 23 has such alength as extending from a left end surface of the annular body 22 to aright end surface of the outer ring 4, and at the same time, has such ashape that it can move in the axial direction in the key groove 2 a ofthe axle box 2. The inwardly projecting part 24 has such a shape that itcannot move in the circumferential direction in the key groove 11 of theouter ring 4, and cannot move inwardly in the axial direction.Accordingly, in FIG. 3, when the length of the rotation shaft 3 hasvaried due to thermal expansion, the outer ring 4 moves in the axialdirection along the axle box 2, whereby the variation due to the thermalexpansion can be absorbed.

An inner diameter of the outwardly projecting part 23 of the key member20 (a length between an axis center of the key member and a radiallyinner surface of the outwardly projecting part) is substantially equalto the outer diameter of the outer ring 4, and when the key member 20 isfitted to the outer ring 4 from the left, the outwardly projecting part23 of the key member 20 is brought into contact with the outerperipheral surface of the outer ring 4, whereby frictional force will begenerated. At the same time, the inwardly projecting part 24 of the keymember 20 is engaged with the key groove 11 of the outer ring 4, wherebythe key member 20 and the outer ring 4 can be handled as an integralbody.

In the above described first and second embodiments, the key members 10,20 are formed of resin such as PEEK (polyetheretherketone). The annularbodies 12, 22, the outwardly projecting parts 13, 23, and the inwardlyprojecting parts 14, 24 are integrally formed by injection molding.

The key member is not necessarily formed of resin, and also notnecessarily formed as an integrally molded product.

Third Embodiment

FIGS. 5A and 5B show the bearing apparatus according to a thirdembodiment of the invention. The third embodiment is different from thefirst and second embodiments in that a key member 30 is composed of twomembers.

The key member 30 in this embodiment includes an annular holding member31 corresponding to the annular body, and an engaging member 32 which isengaged with a groove 35 formed in the annular holding member 31.

The annular holding member 31 includes a cylindrical part 33, and aninwardly directed flange part 34 which is provided at a left end of thecylindrical part 33. The inwardly directed flange part 34 is cut out atone position in the circumferential direction, and the cylindrical part33 continued from the inwardly directed flange part 34 is cut out up toa center position in the axial direction, whereby the groove 35 to beengaged with the engaging member 32 is formed.

As shown in FIG. 5A, the engaging member 32 includes an invertedL-shaped part 36 having a horizontal portion 36 a and a vertical portion36 b and adapted to be engaged in the groove 35, an outwardly projectingpart 37 which extends in the axial direction from an upper part of thehorizontal portion 36 a of the inverted L-shaped part 36 and adapted tobe inserted into the key groove 2 a of the axle box 2, and an inwardlyprojecting part 38 which is provided at a right side of the verticalportion 36 b of the inverted L-shaped part 36 and adapted to be insertedinto the key groove 11 of the outer ring 4.

As shown in FIG. 5B, the annular holding member 31 and the engagingmember 32 which are separate members are assembled, whereby the memberhaving the same shape as the key member 10 as shown in FIG. 2 isobtained. Therefore, by fitting the key member 30 having the annularholding member 31 and the engaging member 32 to the outer ring 4, thesame sectional shape as shown in FIG. 1 is obtained, and the sameoperational effect can be attained as the bearing apparatus 1 in thefirst embodiment.

Fourth Embodiment

FIGS. 6A and 6B show the bearing apparatus according to a fourthembodiment of the invention. The fourth embodiment is different from thesecond embodiment in that a key member 40 is composed of two members.

The key member 40 in this embodiment includes an annular holding member41 corresponding to the annular body, and an engaging member 42 which isengaged with a groove 45 formed in the annular holding member 41.

The annular holding member 41 has a square shape in cross section, andan outer peripheral surface and a right surface thereof are cut out atone position in a circumferential direction, whereby the groove 45 to beengaged with the engaging member 42 is formed.

As shown in FIG. 6A, the engaging member 42 includes an invertedL-shaped part 46 having a horizontal portion 46 a and a vertical portion46 b and adapted to be engaged in the groove 45, an outwardly projectingpart 47 extending in the axial direction from an upper surface of thehorizontal portion 46 a of the inverted L-shaped part 46 and adapted tobe inserted into the key groove 2 a of the axle box 2, and an inwardlyprojecting part 48 positioned at a right side of the vertical portion 46b of the inverted L-shaped part 46 and adapted to be inserted into thekey groove 11 of the outer ring 4.

As shown in FIG. 6B, the same shape as the key member 20 as shown inFIG. 4 can be obtained, by assembling the annular holding member 41 andthe engaging member 42 which are separate members. Therefore, when thekey member 40 composed of this annular holding member 41 and theengaging member 42 is fitted to the outer ring 4, the same sectionalshape as shown in FIG. 3 can be obtained, and the same operationaleffects as in the bearing apparatus in the second embodiment can beattained.

The annular bodies 12, 22, the outwardly projecting parts 13, 23, andthe inwardly projecting parts 14, 24 of the key members 10, 20, and theannular holding members 31, 41, the engaging members 32, 42, theoutwardly projecting parts 37, 47 and the inwardly projecting parts 38,48 of the key members 30, 40 in the above described embodiments can bemodified according to the shape of the axle box 2, and according toeasiness in working the outer ring 4. One of the examples is shown inFIGS. 7 and 8.

Fifth Embodiment

FIGS. 7 and 8 show the bearing apparatus according to a fifth embodimentof the invention.

In the bearing apparatus 1 in a fifth embodiment, the axle box 2 isprovided with a small diameter inner peripheral surface 2 b having aninner diameter which is substantially equal to the outer diameter of theouter ring 4, and a large diameter inner peripheral surface 2 c having alarger inner diameter than the small diameter inner peripheral surface 2b. The outer ring 4 is supported by the axle box 2, in a state where itsleft end part is positioned on the large diameter inner peripheralsurface 2 c and the other part is positioned on the small diameter innerperipheral surface 2 b. The key groove 2 a of the axle box 2 is formedon the small diameter inner peripheral surface 2 b. In addition to thekey groove (an upper key groove) 11 which is formed in the first tofourth embodiments, another key groove (a lower key groove) 15 is formedat a position separated from it by 180 degree. A key member 50 includesan annular body 52 (flange part) in a square shape in cross section andhaving an inner diameter which is substantially equal to the outerdiameter of the outer ring 4 and an outer diameter which is smaller thanthe large diameter inner peripheral surface 2 c of the axle box 2, anoutwardly projecting part 53 extending to the right from an outerperiphery of the annular body 52 and adapted to be inserted into the keygroove 2 a of the axle box 2, an upper inwardly projecting part 54provided in an upper part of an inner peripheral surface of the annularbody 52 and adapted to be inserted into the upper key groove 11 of theouter ring 4, and a lower inwardly projecting part 55 provided in alower part of an inner peripheral surface of the annular body 52 andadapted to be inserted into the lower key groove 15 of the outer ring 4.

There is no difference in working trouble between a work for formingonly the upper key groove 11 extending from the inner diameter to theouter diameter, and a work for continuously cutting the outer ring 4from one outer diameter to the other outer diameter, that is, the workfor forming the upper key groove 11 and the lower key groove 15, andhence, the outer ring 4 in the fifth embodiment can be easily obtainedin the same manner as the outer ring 4 in the first to fourthembodiments. Then, by engaging the inwardly projecting parts 54, 55integrally provided on the annular body 52 respectively with the two keygrooves 11, 15, the key member 50 can be stably fitted to the outer ring4, although the key member 50 has no cylindrical part.

The bearing apparatus 1 in the fifth embodiment can be applied to theaxle box 2 without altering the inner diameter of the axle box 2 and theouter diameter of the outer ring 4, and can attain the same operationaleffects as the bearing apparatus 1 in the second embodiment.

Sixth Embodiment

FIGS. 9 and 10 show the bearing apparatus according to a sixthembodiment of the invention.

In case of working the outer ring 4 formed of ceramics which is brittlematerial, it is also possible to form the outer peripheral surface ofthe outer ring 4 as an eccentric surface. In a bearing apparatus 1 in asixth embodiment as shown in FIGS. 9 and 10, an eccentric surface 4 a isformed on the entire outer peripheral surface of the outer ring 4, byworking the outer peripheral surface of the outer ring 4 so as to make acylindrical surface which is eccentric by D in a downward direction froman axis center. Correspondingly, a key member 60 includes an annularbody 62 which has an inner peripheral surface 62 a along the eccentricsurface 4 a of the outer ring 4 and a cylindrical outer peripheralsurface 62 b having an outer diameter which is substantially equal tothe inner diameter of the axle box 2, and an outwardly projecting part63 provided in an upper part of the outer peripheral surface 62 b of theannular body 62 and adapted to be inserted into the key groove 2 a ofthe axle box 2.

The outwardly projecting part 63 is so shaped as to be movable in theaxial direction in the key groove 2 a of the axle box 2, and therefore,in case where the length of the rotation shaft 3 has varied due tothermal expansion, in FIG. 9, the variation due to the thermal expansioncan be absorbed, since the outer ring 4 moves in the axial directionalong the axle box 2.

In the sixth embodiment, because the eccentric inner peripheral surface62 a of the key member 60 is engaged with the eccentric outer peripheralsurface 4 a of the outer ring 4, the key member 60 can be stably fittedto the outer ring 4. It is of course possible to produce the key member60 as a resin molded product, and to fit this key member 60 to the outerring 4 from the left. However, it is more preferable to produce theouter ring 4 provided with the eccentric surface 4 a on the outerperiphery by molding out of resin, employing the resin molding process,and to obtain the key member 60 which is integrally molded to the outerring 4. In this manner, it is possible to produce the key member 60 andto handle it thereafter, more easily.

Moreover, according to the sixth embodiment, the shape of the axle box 2need not be modified, by making the outer diameter of the key member 60equal to the inner diameter of the axle box 2. Further, because theeccentric surface 4 a need not be provided on the entirety of the outerring 4 (from one end in the axial direction to the other end), theeccentric surface 4 a may be formed only in the left end part of theouter ring 4, while the key groove 11 in the fifth embodiment as shownin FIG. 7 is replaced by an eccentric groove having the same length inthe axial direction as the key groove 11. In this manner, it is possibleto maintain the outer diameter of the outer ring 4.

1. A bearing apparatus to be supported by an axle box which includes akey groove, the bearing apparatus comprising: an outer ring whichincludes a first key groove extending from an inner diameter to an outerdiameter of an axial end surface of the outer ring; an inner ring;rolling elements rollably interposed between the outer and inner rings;and a key member which includes an annular body, a first inwardlyprojecting part which is provided on the annular body and adapted to beinserted into the first key groove of the outer ring, and an outwardlyprojecting part which is provided on an outer periphery of the annularbody and adapted to be inserted into the key groove of the axle box, andwherein the outwardly projecting part extends axially outward of anaxially outermost portion of the annular body.
 2. The bearing apparatusaccording to claim 1, wherein the outer ring includes a second keygroove, and wherein the key member includes a second inwardly projectingpart which is provided on the annular body and adapted to be insertedinto the second key groove of the outer ring.
 3. The bearing apparatusaccording to claim 2, wherein the second inwardly projecting part isdisposed opposite the first inwardly projecting part.
 4. The bearingapparatus according to claim 2, wherein the second inwardly projectingpart is configured so as to extend, in an axial direction of the annularbody, from an axially inward end face of the annular body to an axiallyoutward end face of the annular body.
 5. The bearing apparatus accordingto claim 1, wherein a radially outer periphery of the outwardlyprojecting part is disposed radially outward of the outer periphery ofthe annular body.
 6. The bearing apparatus according to claim 1, whereinthe outwardly projecting part is disposed so as to overlap, in acircumferential direction of the annular member, the first inwardlyprojecting part.
 7. The bearing apparatus according to claim 1, whereinthe outwardly projecting part comprises a square cross section.
 8. Thebearing apparatus according to claim 1, wherein the annular body has aninner diameter substantially equal to the outer diameter of the outerring.
 9. The bearing apparatus according to claim 1, wherein the annularbody comprises a square cross section.
 10. The bearing apparatusaccording to claim 1, wherein the first inwardly projecting part extendsradially inward to the inner diameter of the outer ring.
 11. The bearingapparatus according to claim 1, wherein the outwardly projecting partextends from the annular body to an opposite axial end face of the outerring.
 12. The bearing apparatus according to claim 1, wherein theoutwardly projecting part has a thickness, in a circumferentialdirection of the annular body, less than a circumference of the annularbody.
 13. The beating apparatus according to claim 1, wherein the secondinwardly projecting part comprises a width, in an axial direction of theannular body, substantially equal to a width of the annular body. 14.The bearing apparatus according to claim 1, wherein the axiallyoutermost portion of the annular body comprises an axial end face of theannular body.